The purpose of the present application is to generate the initial preliminary data using diet-induced obesity mouse models of breast cancer on the plausible roles of adipocytes, mammary tumor cells and macrophages in breast cancer pathogenesis. Our hypothesis that adipocytes and mammary tumor cells may play a role in the recruitment of macrophages to the mammary gland contributing to its tumorigenicity is novel, since there is no information regarding the crosstalk between these three cell types in the mammary tumor microenvironment. We will examine the impact of this cellular interplay on macrophage chemotaxis, M1/M2 activation profiles and cell differentiation in vitro, using co-cultures of mouse macrophage, mammary tumor and adipocyte cell lines. Specific signaling inhibitors of paracrine factors produced by adipose or tumor cells will be used to reverse these actions, and proteomics analyses will be undertaken to identify novel molecules secreted by adipocytes and mammary tumor cells with actions on macrophages. Moreover, the impact of blocking the functions of these paracrine factors on mf 's NFkB and STAT3 activation will be studied.. We will also focus on one of these paracrine factors, the adipokine leptin, produced by adipocytes and mammary tumor cells, which has a central role in breast cancer pathogenesis and in macrophage chemotaxis. A novel leptin-signaling inhibitor peptide designed by one of us will be used in in vivo experiments with diet-induced obese mice to reverse primary tumor and metastasis progression and macrophage recruitment in these animals implanted with syngeneic C57BL6 mammary tumors. We envision that results from the present proposal will ultimately provide original information that will lay the foundation to initiate similar studies in breast cancer in African American (AA) and Latina (LA) women in the future. A high-fat diet, overweight and reduced physical activity are common lifestyle aspects among AA and LA that increase cancer risk;these women also exhibit more aggressive breast cancers with less favorable outcomes. The experiments proposed in this application address for the first time the interaction between these three cell types within breast tumors. There is an urgent need to build up studies to better understand the biology of cancers across ethnicities, and to develop tools to more accurately predict their prognosis and design their customized treatment strategies. PUBLIC HEALTH RELEVANCE: The proposed studies will increase our understanding on how the actions of adipose tissue on the mammary gland may promote breast cancer through macrophage recruitment and expression of important ligands/receptors. This could lead to new ways of breast cancer prevention and/or therapeutic alternatives for overweight/obese women, especially African American and Latinas, characterized by high prevalence of obesity/overweight and more aggressive breast cancers with worst prognoses.